Preliminary assessment of trends in static water levels in bedrock wells in New Hampshire, 1984 to 2007

Abstract

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. iii AcknowledgmentsThe authors acknowledge the support and input of the drilling and environmental-science communities in the development of this report. Special thanks are extended to the drilling industry for their effort in providing well-completion reports and to the NHDES staff, particularly Richard Schofield and Frederick Chormann, who have over the years carefully managed these data. Thanks also to Allen Shapiro, Rodney Sheets, Leslie DeSimone, and Dennis Risser of the USGS for discussion of data and analyses. Mary Ashman edited the report, M. Patricia Lee and Mark Bonito provided layout and graphic assistance. AbstractAnalysis of nearly 60,000 reported values of static water level (SWL, as depth below land surface) in bedrock wells in New Hampshire, aggregated on a yearly basis, showed an apparent deepening of SWL of about 13 ft (4 m) over the period . Water-level data were one-time measurements at each well and were analyzed, in part, to determine if they were suitable for analysis of trends in groundwater levels across the state. Other well characteristics, however, also have been changing over time, such as total well depth, casing length, the length of casing in bedrock, and to some extent, well yield. Analyses indicated that many of the well construction variables are significantly correlated; the apparent declines in water levels may have been caused by some of these factors. Information on changes in water use for the period was not available, although water use may be an important factor affecting water levels.Multiple regression models were used to determine the simultaneous effects of important variables on SWLs statewide. Models also were generated for each county, and the model-calculated results for counties were generally similar to the results for the state wide models.The most significant predictors of mean SWL (aggregated by year and quarter) were total depth, the third quarter of the year (July-September), elevation, and height of well above minimum elevation within a 1,640-foot (500-meter) radius (hillslope factor). Casing length was a significant predictor of SWL for igneous-rock models and curvature of the land surface for metamorphic-rock models. Local geologic as well as landscape features appear to provide further explanation of SWL variation. For example, SWLs in wells completed ...

Assessing Models of Arsenic Occurrence in Drinking Water from Bedrock Aquifers in New Hampshire

“…Deep wells with long casings, drilled through deep bedrock fractures, facilitate the collection of old groundwater, which is typically alkaline and has arsenic concentrations leached from adjacent bedrock fracture surfaces. As groundwater well systems have increased in casing length and depth by an average of nearly 1 foot and 6 feet per year, respectively, over the past 30 years, the age of the well may also bear an effect on arsenic content in acting as a surrogate explanatory variable for aquifer depth (Ayotte et al ). Although the age of the well was not reported in either the model training or testing datasets, it is possible that this explanatory variable is influential in predicting arsenic occurrence.…”

Identification of Groundwater Nitrate Contamination from Explosives Used in Road Construction: Isotopic, Chemical, and Hydrologic Evidence

“…Thin (<3 m) glacial till overlies igneous and metamorphic bedrock in the study area . The bedrock is Silurian-age metasedimentary rock intruded by multiple phases of Devonian-age granite. − A potentiometric-surface map (Figure ) was produced from existing water level-data, − topography, and surface water features. In general, groundwater flow was southward through the till and fractured bedrock toward Cobbetts Pond but with considerable local variation related to topography.…”